Net Income per Share (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Earnings Per Share [Abstract]
Net income	$ 3,488	$ 5,621	$ 16,661	$ 19,505
Less distributed and undistributed earnings allocated to participating securities	(124)	(162)	(481)	(564)
Net income allocated to common shareholders	$ 3,364	$ 5,459	$ 16,180	$ 18,941
Weighted average common shares outstanding (in shares)	24,820	25,095	24,858	25,091
Incremental shares from assumed conversions of common stock options (in shares)	24	60	27	66
Adjusted weighted average common shares outstanding (in shares)	24,844	25,155	24,885	25,157
Potentially dilutive securities not included in weighted average share calculation due to anti-dilutive effect (in shares)	16	42	16	29